The present invention relates to improved metal end shells for use in producing easy opening ends for beer and beverage cans. An end shell of this invention has an improved profile that facilitates metal savings while maintaining commercial requirements for buckle resistance of the manufactured easy opening ends as packed on pressurized cans. This invention facilitates use of aluminum sheet material having average longitudinal yield strengths of about 53.5 ksi in the manufacture of the end shells and easy opening ends and therefore facilitates the use of thinner gauge metal.
The desirability of reducing metal usage in can ends for pressurized beer and beverage cans has been well recognized for at least thirty years. Many patents have been granted on various end shell and easy opening end designs and methods of manufacture for achieving such reduced metal usage.
Most commercial end shells for pressurized beer and beverage ends today are formed by a so-called free forming or semi-free forming technique in which the countersink bead in the end shell is formed by causing the metal to be rolled into the shape of the countersink bead as is illustrated and described in U.S. Pat. No. 4,109,599 in the name of Freddy R. Schultz. According to the teaching of that patent, a first supporting tool is moved against the exterior surface of the peripheral end curl and a second stationary supporting tool is applied against the interior surface of the central wall portion to cause the countersink or reinforcing channel to form in the end shell. The free forming technique of the Schultz patent has enabled the use of higher yield strength aluminum alloys (50 ksi and higher) and reductions in metal gauge while maintaining buckle resistance against relatively high pressures in containers. FIG. 1 hereof shows a typical commercial end shell formed by such a technique. As shown in that figure, the end shell has a central wall portion 10, an inner wall 80, an annular groove 78, a frustoconical portion 14 and a peripheral flange 16. In a preferred embodiment, the central wall portion is disposed at a height h of from 0.070-0.090 inch above the bottom of he annular groove 78.
U.S. Pat. No. 6,065,634 to Brifcani et al. discloses a can end and method for fixing it to a can body using less metal, while still permitting stacking. FIG. 2 hereof is representative of end shells made in accordance with the Brifcani et al patent. The can end has its chuckwall 24 inclined to vertical at an angle Cxc2x0 between 20xc2x0 and 60xc2x0, and preferably between 40 degrees and 45 degrees, and has a concave bead (or countersink) 25 with a radius r3 less than about 0.75 mm (0.0295 inches). The can end is preferably made from a laminate comprising an aluminum magnesium alloy sheet such as 5182 or an aluminum manganese alloy such as 3004 with a layer of polyester film on one side. Table 2 in the patent includes dimensions of end shells made in accordance with the patent as having a countersink height h2 of 6.87 mm (0.270 inch) to 7.37 mm (0.290 inch), a panel height h3 in a range of 2.39 mm (0.094 inch) to 2.80 mm (0.114 inch), and a lower chuckwall height h4 in a range of 2.29 mm (0.09 inch) to 2.74 mm (0.11 inch).
WO 98/34743 (A1) in the name of Carnaudmetalbox PLC illustrates and describes an unseamed can end and a method of reforming it similar to that disclosed by U.S. Pat. No. 6,065,634 except that the chuckwall has two parts comprising a first (upper) part inclined to vertical at an angle between 1xc2x0 and 39xc2x0 and a second (lower) part inclined to vertical at an angle of between 30xc2x0 and 60xc2x0. The first part of the chuckwall is deformed during a seaming operation to be substantially vertical as constrained between the seaming roll and the cylindrical sidewall of the chuck.
U.S. Pat. Nos. 4,217,843 and 4,448,332 to Kraska disclose a metal end shell and method and apparatus for forming it from sheet metal having reduced thickness. FIG. 3 hereof represents Kraska""s end shell which has a countersink 20 having a radius R1 less than three times the metal thickness, a depth H of at least 0.075 inch, and an outer wall 24 in the countersink having an angle B that is preferably less than five degrees to a vertical plane P. The end shell further has a second wall portion 34 defined by an angle C that is preferably at least six times greater than angle B. A peripheral curl 12 and central panel portion 14 border the countersink 20 and wall portion 24. The patent states that several million 209 diameter ends were made in accordance with the invention from 0.012 gauge 5182-H19 aluminum in which the finished ends have a radius R1 of approximately 0.030 inches, an angle B of approximately 4 degrees and an angle C of approximately 25 degrees.
Other end shell profiles and techniques for reducing metal usage while maintaining acceptable buckle resistance are disclosed in U.S. Pat. No. 6,102,243 (Fields et al.), U.S. Pat. No. 6,089,072 (Fields), U.S. Pat. No. 5,685,189 (Nguyen et al.), U.S. Pat. No. 5,046,637 (Kysh), U.S. Pat. No. 4,991,735 (Biondich), U.S. Pat. No. 4,809,861 (Wilkinson et al.), U.S. Pat. No. 4,606,472 (Taube et al.), U.S. Pat. No. 4,093,102 (Kraska), and U.S. Pat. No. 3,843,014 (Caspen et al.); and Japanese Utility Model No. 2,544,222, among others.
Despite the significant progress that has been made in reducing the gauge of metal used in end shells while maintaining buckle resistance, further enhancements are needed that will facilitate the uses of higher yield strength metal in such end shells and thereby facilitate greater metal savings.
This invention is particularly addressed to end shells that are to be converted into easy opening ends for beer and beverage cans, and to such converted ends suitable to be double seamed on aluminum can bodies. Most end shells and can ends in commercial use today are made of hard temper aluminum alloys, most of which alloys contain magnesium in a range of about 4.0 to 5.0 weight percent. For example, most easy opening ends for beer and beverage containers are currently made of 5182 aluminum alloy containing about 4.5-4.7 weight percent magnesium. Continual improvements in these aluminum alloys and their manufacture into sheet material are producing materials of higher longitudinal yield strength and ultimate strength. Such higher yield strength alloys provide opportunities for reducing metal usage through gauge reduction. One such alloy is 5019A aluminum alloy, as registered with the American Aluminum Association. That alloy contains a nominal weight percent of magnesium of 4.9, and has an average longitudinal yield strength of 53.5 ksi.
Can end diameters for beer and beverage cans have been getting smaller in order to reduce metal usage in the ends. Can end sizes are conventionally described in terms of inches and sixteenths of inches, such that a can end having a diameter of 2{fraction (6/16)} inches, for example, is referred to as a 206 diameter can end. A 202 diameter can end has a diameter of 2{fraction (2/16)} inches. Most beer and beverage can ends today are 204 and 202 diameters.
This invention is addressed to maintaining commercially required buckle resistance of can ends. Buckle resistance means the resistance of can ends to being permanently deformed by internal pressure in packed cans on which the ends are double seamed. Beer ends typically must be able to resist pressures of at least about 92 psig in the cans, and beverage ends typically must be able to resist pressures of at least about 90 psig.
A feature of end shells of this invention is that they have reduced age buckle losses, which are losses in buckle resistance following manufacture of the end shells and easy opening can ends. As used herein, age buckle losses means the loss in buckle resistance within a certain number of days, such as 30 or 90 days, after manufacture of the end shells and ends. Excessive age buckle losses are a known shortcoming of current end shells since the losses make it difficult for manufacturers to predict the eventual buckle resistance of their can ends.
This invention provides a metal end shell having an annular countersink bead around a central panel portion, a substantially vertical lower chuckwall portion in the countersink bead, an upper chuckwall portion extending upwardly and outwardly from the lower chuckwall portion at an angle of about 20-35xc2x0 to vertical, and a curved peripheral flange for double seaming to a container wall. The countersink bead has an internal width of about 0.020-0.040 inch and the end shell has a countersink depth less than about 0.250 inch.
This invention provides a metal end shell profile that can be formed with a low draw ratio, thus permitting the use of higher yield strength metal.
Accordingly, it is an object of this invention to provide a metal end shell having commercially acceptable buckle resistance with reduced metal usage.
Another object of this invention is to provide an end shell that facilitates use of higher yield strength metal.
A further object of this invention is to provide a metal end shell that has reduced buckle losses during aging.
Another object of this invention is to facilitate the use of thinner gauge metal in end shells for pressurized containers.
A further object of this invention is to provide an end shell that is easier to form and which can be formed with a low draw ratio and with a shorter press stroke.
Another object of this invention is to provide an end shell that can be formed from a sheet metal disc having a reduced cut edge diameter.
A further object of this invention is to provide an end shell on which additional forming operations may be performed to enhance the performance characteristics.
The above and other objects and advantages of this invention will be more fully understood and appreciated with reference to the following description and the drawings attached hereto.